A roller bearing disclosed in Patent Literature 1 has been known as a roller bearing capable of bearing both axial loads applied in a direction parallel to a rotation axis of an inner ring and an outer ring, and radial loads applied in a direction orthogonal to the rotation axis. In this roller bearing, rolling passages for rollers are formed between the outer ring and the inner ring along a circumferential direction of the roller bearing, and the rollers are revolved while turning on their axes in the rolling passages along with relative rotational movement between the outer ring and the inner ring.
Specifically, in the roller bearing illustrated in FIG. 5 of Patent Literature 1, two raceway grooves each having a V-shape in cross-section are formed in an inner peripheral surface of the outer ring, whereas two raceway grooves each having a V-shape in cross-section are formed also in an outer peripheral surface of the inner ring. Those raceway grooves face each other so that the pair of rolling passages is formed between the outer ring and the inner ring. The turning axes of the rollers arrayed in each of the rolling passages are inclined at an angle of 45° with respect to the rotation axis of the inner ring and the outer ring. Further, turning axes of the rollers arrayed in one of the rolling passages and turning axes of the rollers arrayed in another one of the rolling passages are orthogonal to each other. With this, the rollers arrayed in the rolling passages are each capable of bearing both the axial load and the radial load.
However, in the roller bearing as illustrated in FIG. 5 of Patent Literature 1, the turning axes of the rollers are inclined with respect to the rotation axis of the inner ring and the outer ring, and hence the rollers differentially slide when the rollers roll between the outer ring and the inner ring. Thus, frictional heat is generated between the rollers and the raceway grooves in use of the roller bearing, with the result that the inner ring and the outer ring are thermally expanded. In this case, the outer ring and the inner ring are each formed into an annular shape, and hence diameters of the outer ring and the inner ring are increased due to the thermal expansion. This phenomenon more conspicuously occurs as the diameters of the outer ring and the inner ring are larger. Note that, although thicknesses of the outer ring and the inner ring are also increased due to the thermal expansion, the increase in thickness is significantly smaller than the increase in diameter because the thicknesses of the outer ring and the inner ring are smaller than circumferential lengths of the outer ring and the inner ring.
In many cases, the roller bearings as described above are used under a state in which an outer peripheral surface of the outer ring is covered with a housing of, for example, a mechanical device, whereas the inner ring is fixed to a rotation shaft. In such cases, deformation of the outer ring in a radial direction is suppressed by the housing, but the inner ring is thermally expanded toward the outer ring suppressed from being displaced in the radial direction. As a result, a force of press contact between the outer and inner rings and the rollers are increased. Thus, frictional heat to be generated between the rollers and the outer and inner rings is increased, which causes such a vicious cycle that additional thermal expansion of the inner ring and the outer ring occurs to excessively increase the force of the press contact between the outer and inner rings and the rollers. In this way, there arises a problem in that smooth rotational movement between the inner ring and the outer ring is hindered.
Meanwhile, in the roller bearing illustrated in FIG. 2 of Patent Literature 1, the turning axes of the rollers are not inclined with respect to the rotation axis of the outer ring and the inner ring. A rolling passage in which rollers configured to bear only the axial loads are arrayed, and a rolling passage in which rollers configured to bear only the radial loads are arrayed are formed independently of each other.
However, in the roller bearing constructed as described above, in order to prevent separation of the outer ring from the inner ring, two rolling passages in which the rollers configured to bear only the axial loads are arrayed need to be formed. As a result, three rolling passages for rollers need to be formed, and hence the thickness of the outer ring needs to be set larger, which is inappropriate in downsizing double-row roller bearings. In addition, the roller bearing has the two rolling passages in which the rollers configured to bear only the axial loads are arrayed, and thus the roller bearing is intended mainly to bear the axial loads. In view of this, it is hard to say that versatility is high.